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Fields irrigated by water from aquifers 1 km under the desert (Credits: NASA/Landsat/ Robert Simmon and Jesse Allen)

Around 11% of non-renewable groundwater used for irrigation is embedded in international food trade, new research shows. Scientists at the University College London and NASA's Goddard Institute of Space Studies found that Pakistan, the US and India are the countries exporting the most crops that depend on non-renewable aquifers. The study, published in the journal Nature on March 29, determines which specific crops come from groundwater reservoirs that won’t renew on the scale of a human life-time, where they are consumed and which products and countries have the biggest impact. The reserachers used FAO trade data on countries’ agricultural commodities and combined it with a global hydrologic model to trace the sources of water used to produce 26 specific crop classes. Their results show that the crops using the biggest amounts of non-renewable groundwater are rice (29%), followed by wheat (12%), cotton (11%), maize (4%) and soybeans (3%). Two-thirds of the exported food that depends on non-renewable groundwater are produced in Pakistan (29%), the United States (27%), and India (12%). In these countries, the amounts of exported crops produced using unsustainable groundwater increased remarkably between 2000 and 2010. In India, exports of groundwater-depleting crops doubled in that period. The amount increased by 70% in Pakistan and by 57% in the US.

According to the researchers, the major importers include the United States, Iran, Mexico, Japan, Saudi Arabia, Canada, Bangladesh, the United Kingdom, Iraq, and China. These countries turned from net exporters in 2000 to net importers in 2010. “It's not just individual countries that experience groundwater depletion, but also their trade partners,” said lead author Carole Dalin of the University College London. “When people consume certain imported foods, they should be aware that they can have an impact on the environment elsewhere.” The study warns that countries that export and import crops that depend on non-renewable aquifers may be at risk of losing these crops and their profits in the future. Co-author Michael Puma gives the example of Japan importing corn from the United States: “It's important from Japan’s perspective to know whether that corn is being produced with a sustainable source of water, because you can imagine in the long term if groundwater declines too much, the United States will have difficulty producing that crop.” The researchers say that their results can help target efforts to improve the sustainability of water use and food production. Decision makers and local farmers will need to decide on a strategy for using non-renewable water resources that balance the needs of short-term production versus long-term sustainability. The study lists solutions to minimize groundwater depletion. Water-saving strategies in the producing countries include improving irrigation efficiency and growing more drought-resistant crops, together with measures such as the regulation of groundwater pumping. (ab)